Last year's draft was the draft of the decade, but, even so, the Spurs had only 20 players graded out as first rounders, per RC Buford. Kyle was one of them, yet they got him at 30. Spurs obviously didn't think he'd be there, either, so he was in good company.
If you look at his stats from December when he was getting rotational minutes, they jump off the page at you. He shot 50%, way better than his seasonal FG%. He was never going to get rookie minutes, other than covering for Kawhi's injury time, on a team defending it's le. He will this year, and he will produce. He didn't just go to the d-league, he crushed it there with 21.5ppg/8.7r/4.8a/2.0st/1.5bl, exactly what you want to see from an assigned player.